This invention relates to an exposure meter for use by photographers and arose with a view to providing an indication of the distribution of luminance values over a field of view, rather than just the luminance of one particular part of the field of view.
We did endeavor to meet this requirement in the past using a somewhat unconventional arrangement described in our Patent Specification GB No. 693443. This displays a graph of brightness vs. horizontal angle of view. The value of the horizontal angle of view is however of no value to the user of the instrument and the brightness values, being only average values for vertical strips of the field of view, are of limited value since they could include bright areas of sky and dark shadows on the ground.
A conventional spot exposure meter has a narrow field of view compared with a scene to be photographed and provides a single output measurement representing the luminance of one particular part of the scene. In order to obtain an indication of the contrast of the scene the conventional spot exposure meter must be pointed in successive different directions and the different measurements obtained must be noted by the photographer. In a more sophisticated known system the exposure meter has a wider field of view covering the whole of a scene to be photographed and includes six photocells which provide respective luminance values for six shaped sectors of the field of view. A decision on the required exposure is made automatically on the basis of the six measured values, knowledge of the type of scene (e.g., portrait, outdoor daylight scene etc.) which is entered manually by the photographer, and various assumptions concerning the likely content (e.g. sky) and photographic importance of features in the different sectors. This automatic system is recognized as suffering from certain drawbacks. For example it does not allow for unusual types of scene or for the achievement of special dramatic or unusual photographic effects. For these reasons a special switch is provided to prevent the above automatic system from operating when not required.